Golf club heads are typically constructed of metal and must be manufactured to precisely the correct weight. Golf club heads are typically metal castings which are appropriately finished to provide the desired club head contour and finish. Controlling the weight of the casting is very difficult due to shrinkage and variations in the pattern thickness. In addition, the process of finishing the casting removes varying amounts of material from the golf club heads. For these reasons, golf club heads, at this stage of production, are not at the correct weight.
Many golf club heads, such as metal woods, are hollow and have a wall which defines an interior chamber and a hosel leading to the chamber. It is customary to fill the chamber with foam plastic after finishing of the casting. This adds weight but, in many cases, not a sufficient amount to bring the club head to the desired weight.
To increase the amount of weight added to the club head, particulate material, such as silica sand or lead filings, are introduced into the chamber through the hosel prior to the introduction of the foam plastic. Before the foam plastic cures, the club head is agitated in an attempt to distribute the particles throughout the foam. Unfortunately, many of the particles do not become trapped in the foam and rattle. In addition, the relatively heavy particles which are trapped in the foam tend to break loose during use of the club head. Also, some of the particles may be trapped within a relatively large void within the foam plastic. All of these loose particles within the club head rattle during use, and this may cause the club to be returned to the manufacturer. Finally, it is not possible to control the distribution of weight inside the club head using this technique.
Attempts have also been made to weight a golf club head with an epoxy adhesive. However, the epoxy is very difficult and messy to inject, and it is somewhat difficult to accurately control the weight of the epoxy which is injected. Furthermore, after curing, the epoxy becomes very hard and brittle and tends to break off and rattle inside the club head.